As the functionality of extremity prostheses is advanced, increasing loads will be induced into the total prosthesis system. These loads must be isolated from the residual limb of the person, or alternatively reacted into the appendage or amputation point of the residual limb in a controlled manner. Many current prosthetic devices, which are often a socket-type arrangement, shed their loads principally into the skin of an appendage or into the skin of a torso, via belt-strap-buckle attachments or other mechanical fastening devices. Significant loading of the skin typically provides an inferior mechanical foundation for the prosthesis system. An inferior mechanical foundation may prove inadequate for the prosthesis to function properly, or too compliant to support the induced loads. Further, conventional systems create discomfort for the person, damage the skin, and/or permanently stretch the skin. Using belts, straps, etc. that pass around the torso or appendage of a person results in a large, bulky, heavy and uncomfortable prosthesis system that creates an unnatural appearance that is strongly disfavored by the wearer. Compliance of existing systems is typically too high, resulting in unwanted and uncontrolled prosthesis slip during use, even with relatively lightly loaded prostheses.
The human skeleton supports loads from the extremities of the body, therefore, when the loads can be properly translated to the skeletal structure a more robust prosthesis system can be envisioned. Osseointegration is a natural response of the body that can help with this load translation, thereby addressing at least some of the mechanical deficiencies associated with current prosthesis systems. With osseointegration, foreign objects introduced into the body (for example a titanium implant placed into a cavity of a bone such as the femur) are not only accepted by the body and brain, but become an integral part of the body structure.
The genetic codes within the body that typically would direct the body to reject the foreign object are not, in fact, activated. Instead, bone cells attach to the surface of the foreign object (e.g. titanium implant) resulting in a firm and permanent anchorage of the implant to the bone. Unfortunately, existing prosthetic devices that capitalize on the natural phenomenon of osseointegration typically involve a permanent and constant penetration of the skin. Permanent skin penetration often leads to short and long term infection issues, requiring enhanced care by the individual.
While there are existing systems that employ magnetic materials and devices implanted below the patient's skin, these devices are not typically designed to robustly and magnetically couple the prosthetic device to the residual limb, while controlling multiple loads from multiple orientations. One such device known in the prior art is U.S. Pat. No. 5,879,386 to Jore, “Magnetic Prosthesis System”. The need to use straps, buckles, etc. to affix the prosthesis to the appendage, and to control prosthesis movement, is still present. Further, the permanent magnetic fields established by implanted magnetic materials and magnets within a prosthesis cannot adapt and change to varying loads and functional movements of the prosthesis.
Hence there is a need for a prosthesis system to address one or more of the drawbacks identified above.